VITAMINS

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Recent progress in the fields of arginine-specific ADP-ribosyltransferases (ADPRT) and target proteins has been rapid and extensive, and the importance of monoADP-ribosylation in eukaryotic cells under physiological conditions is now widely accepted. ADPRT from chicken peripheral polymorphonuclear granulocytes (heterophils) and its target proteins have been characterized by enzymatic and molecular analyses. The properties of the heterophil enzyme differ from those of turkey erythrocytes and rabbit skeletal muscle ADPRT which have been purified and extensively studied. Although heterophil enzyme can modify a number of proteins in vitro, p33 (33 kDa protein) and β/γ-actin are considered to be in situ substrates for the ADPRT, since both proteins were modified when the cells permeabilized with saponin were incubated in the presence of NAD. The sequence of p33 proved to be identical with the regions of amino acid sequences deduced from myb-induced myeloid protein-1 cDNA (Cell, 59, 1115-1125, 1989). The ADP-ribosylation of G-actin inhibited the capacity of the protein to polymerize. Based on the obtained amino acid sequences of the enzyme purified from heterophils, two arginine-specific ADPRT cDNA (CHAT1 and CHAT2) were obtained from chicken bone marrow cells. Homology of the deduced amino acid sequences between CHAT1 and CHAT2 was 78.3%. ADPRT activity was detected in culture medium of COS 7 cells transiently transfected with CHAT1 cDNA, while activity from the cells transfected with CHAT2 was present in both culture medium and cell lysate. Both enzymes showed different properties with respect to the effects of 2-mercaptoethanol and NaCl on the activity, in which CHAT1 enzyme showed much the same properties with the native enzyme purified from heterophils. The similarity of deduced amino acid sequences around the active site glutamic acid of chicken bone marrow cell ADPRT was observed in mammalian skeletal muscle and chicken erythroblast ADPRT, and also in the related proteins, rodent RT6.

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The effect of biotin-supplemented diet, on the blood glucose level and the serum biotinidase activity, was investigated in streptozotocin-induced diabetic rats. Rats were fed diets, with or without 0.02% biotin for 7 days. Biotinidase activity was measured by several biotin-amides and leucine-enkephalin, as substrates. Blood glucose level was improved by the biotin-supplemented diet, compared with the diabetic rats. The serum biotinidase activity as measured by biotin-amides substrates in the diabetic rats was not changed at all, and was independent of the biotin supplement. Leucine-enkephalin hydrolysis activities were higher than the controls, but these increments were not affected by the biotin-supplemented diet. There was a significant inverse correlation between blood glucose level and biocytin hydrolysis activities in the diabetic rat (r=-0.673, p<0.05), but no correlation in the biotin supplemental group. These results indicate that serum biotinidase in diabetic rats may have been modified by glucose, and this possible modification by glucose may be suppressed by supplementing dietary biotin.

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